Arecibo radar observations of dwarf planet Ceres during the 2018 Apparition

We report dual-polarization, Doppler-only radar observations of dwarf planet (1) Ceres that were obtained using the Arecibo planetary radar system (2380 MHz, 12.6 cm) during 2018 February 20 - 27. Each evening's observations comprised two runs, each consisting of a continuous-wave (CW), circularly polarized transmission lasting 27 min. This was followed by receiving the Doppler-shifted echoes for an equal time, simultaneously in the same sense of circular polarization (SC) as transmitted and the opposite (OC) sense. The total of 9 runs yielded six valid echo power spectra. The weighted average of the individual spectra obtained at different asteroid rotation phases yielded an OC radar cross section of 2.52 ± 0.2x10⁴ km², radar albedo of 0.036, and Circular Polarization Ratio (CPR) of 0.024, consistent with the 1986 Arecibo radar observations of Ceres [1]. A variation of 10% in radar cross section was observed over the approximately 210° of apparent rotation phase. The Dawn spacecraft has gathered important data about the surface composition, internal structure, and geomorphology of Ceres. Ground-based radar observations compared with orbiter-based data may reveal insights to the near surface of Ceres. References: [1] Mitchell et al., 1996, Icarus, 124, 113-133